In recent years, thin films of certain species of metal chalcogenides, such as titanium disulfide (TiS.sub.2) and other transition metal sulfide materials have been studied. Films of TiS.sub.2 may be formed using chemical vapor deposition (CVD) methods, by sulfurization of titanium metals at elevated temperatures, and sputtering methods.
A number of CVD processes have been described by the prior art. Deficiencies in such methods were discussed in the parent case which is herein incorporated by reference. Typically in these prior art processes, gaseous streams of the two reactants (i.e. titanium tetrachloride and hydrogen sulfide) are mixed in a heated reactor to deposit the desired metal chalcogenide as a film on a substrate suspended in the reactor. It is often necessary in these processes to use a large excess of the chalcogenide source (i.e. H.sub.2 S) in order to achieve reasonable deposition rates. Moreover, the chemical yield of the films in such cases is often extremely low. This results in the waste of most of the agents required to form the film, which in turn, leads to an inefficient process with concomitant toxic waste problems.
It would be highly desirable to have a volatile single source precursor capable of being sublimed into the CVD reactor to deposit the film. Ideally such precursors would contain the correct stoichiometry of elements needed for the metal chalcogenide film and would minimize waste materials. Unfortunately, however, the prior art has been unable to provide such a material and no single source precursor to CVD titanium disulfide films has been reported in the literature.
The most important commercial application for titanium disulfide films is as cathodes in lithium batteries. In such an application it is highly desirable that the thin film of TiS.sub.2 have a crystallographic orientation such that the c-axis is parallel to the plane of the substrate. In such an orientation, pores in the crystals are perpendicular to the plane of the substrate and are optimum for the intercalation of lithium, which constitutes the primary discharge reaction in the lithium battery. Conversely, an orientation in which the pores of the crystals are parallel to the plane of the substrate leads to an inefficient cathode reaction, due to poor intercalation of lithium ions into the TiS.sub.2.
It has been demonstrated by Kikkawa et al. (J. Mater. Res. 1990, 5, 2894) and Kanehori et al. (J. Electrochem. Soc. 1989, 136, 1265) that TiS.sub.2 films with predominant (110) crystallographic orientation provide optimum cathode performance in a lithium battery. However, such preferred films with the highly desirable (110) orientation have only been prepared from CVD techniques using two separate gaseous streams of titanium tetrachloride and hydrogen sulfide and thus incorporate all of the prior art limitations, including the undesirable deposition characteristics discussed above.